Adaptation in Animals


Our objective is to study the characteristics of the following animals: earthworms, cockroaches, bony fish and birds.

Furthermore, for each specimen we need to identify:

  1. Specific features of its phylum
  2. Adaptive features with reference to its habitat.

The Theory

Animals are multicellular organisms that are made up of eukaryotic cells and come under the kingdom Animalia. They have a well developed sensitive nervous systems and the ability of locomotion. Animals need to ingest other organisms, or their products, for sustenance because they do not perform photosynthesis.

Animals are adapted to the conditions of the habitats in which they live. There are three major types of habitat:

  • Terrestrial (land)
  • Aquatic (water)
  • Aerial or arboreal (air or tree)

Animals also depend on their physical features to help them move about, obtain food, and keep safe.  These physical features are called physical adaptations. Based on their physical characteristics, the Kingdom Animalia is divided into two sub-kingdoms:

  1. Invertebrates
  2. Vertebrates


Invertebrates are animal species that do not have a backbone or spinal column. This, in effect, includes all animals apart from the subphylum Vertebrata. Some common examples of invertebrates include insects, worms, clams, crabs, octopus, snails, and starfish.


Vertebrates are animal species that have a backbone or spinal column. These include jawless fish, bony fish, sharks and rays, amphibians, reptiles, mammals, and birds.

Shown below is a broad classification of the animal kingdom.

Characteristics of some animals based on their phylum and adaptations:

We will now look at the characteristics of some animals based on their phylum and adaptations.


Phylum: Annelida; Habitat: Subsoil (Terrestrial)

The earthworm has a long cylindrical body that is covered by a moist, protective cuticle. The body of an earthworm is segmented and these segments are called Annuli. The body wall has three cell layers-  ectoderm (outer layer), mesoderm (middle layer) and endoderm (inner layer).

The Clitellum is a thickened glandular section of the body wall in earthworms and leeches that secretes a viscid sac in which the eggs are deposited. The body wall has a moist secretion that makes the skin slippery and moist so that soil does not stick to the skin. All annelids except leeches have tiny hair like bristles called setae, projecting from their cuticle.

The setae are composed of chitin. It is the setae that help the earthworm to attach itself to the ground and prevent it from sliding back during peristaltic movement. The body is flexible, as it has no skeleton. At one end is the mouth which is covered by a flap, called the prostomium.  The prostomium helps the earthworm sense light and vibrations, as it has neither eyes nor ears. At the other end is the anus through which waste is excreted.

Specific features of Phylum Annelida

  • The exterior and interior of the body is segmented.
  • Moist secretions make the skin of the earthworm slippery and moist.
  • It has chitinous setae on its body.


  • The earthworm’s skin is brown coloured like the colour of mud. This gives it protection from its enemies.
  • It feeds on humus, which is the rich organic matter found in soil.
  • The body of an earthworm is long, cylindrical and symmetrical. These features help it to burrow into the soil.
  • The earthworm eats the soil that comes in its way and excretes it through the nephridia, found on each segment.


Phylum: Arthropoda; Habitat: Terrestrial

A cockroach has an externally segmented body divided into three main parts- the head, thorax and abdomen. Its body is protected by an exoskeleton of a thick cuticle made of chitin. The head bears compound eyes that allows the cockroach to see simultaneously in all directions. It has a pair of long antennae that helps it to smell.

The thorax has three segments.  Each segment bears a pair of jointed lateral appendages that helps it in movement. The last two segments of the thorax have two pairs of wings which help it to fly short distances.

It has holes, called spiracles, in its thorax and abdomen to take in atmospheric oxygen. There are two wind sensitive hairs called cerci on the last segment of its body. These act as a warning system against its enemies. A flattened body allows it to creep into very narrow crevices. Cockroaches are omnivorous and are nocturnal. They come out of their hiding places at night in search of food.

Specific features of Phylum Arthropoda

  • A cockroach has jointed appendages (legs) like all arthropods.
  • A cockroach has an externally segmented body with a distinct head.
  • Like all arthropods, a cockroach is an invertebrate animal having an exoskelton.


  • Cockroaches live in dark, moist and warm places, such as gutters and drains.
  • A cockroach is dark brown in colour, which helps it to hide in dark spaces and crevices.
  • It has a flattened body that helps it to squeeze into narrow spaces.
  • The head has a pair of long sensitive antennae which help it to smell food.
  • It has a versatile mouth part that helps it to eat all types of foods.
  • On sensing danger, it can hide by running very fast on its legs, or fly short distances to escape.

Bony Fish

Phylum: Chordata; Subphylum: Vertebrata; Class: Pisces; Subclass: Osteichthyes; Habitat: Aquatic

Bony fish are found in marine and fresh water. They have a stiff bony skeleton and like all fishes, their heart is two chambered.

A streamlined body helps in movement by cutting through water easily. It has fins that helps it to change directions in its movement. The body is covered with scales that help prevent decay from water.

Gills on the either side help to breathe in air. A flap called operculam on each side of the head covers the gills, and allows air to enter the gills. The internal air sac or air bladder makes the fish more buoyant and keeps it afloat. It senses pressure of water with the lateral line system, a special sense organ, which enables it to 'touch' objects at a distance.

A muscular tail extends backward behind the anus. Fishes are cold blooded aquatic animals.

Specific features of Phylum Chordata (Class: Pisces)

  • The bony fish has a stiff body skeleton.
  • It has a strong vertebral column that encloses the spinal cord.
  • Like other features of the class Pisces, the exoskeleton is in the form of scales.
  • The endoskeleton is bony, a feature seen in the subclass Osteichthyes.
  • The bony fish has a flap called the operculum on each side of the head that covers the gills.
  • The vertebral column ends with a caudal fin.
  • Fish are cold blooded.


  • The bony fish is adapted to live in salty, as well as fresh water.
  • It has a streamlined body that helps it to easily cut through water, and fins that help it to change direction.
  • Its body is covered with scales, which prevents decay due to water.
  • An air bladder helps the bony fish to float, and a lateral line system helps it to sense the pressure of water.
  • Operculum prevents water from entering the gills.


Phylum: Chordata; Subphylum: Vertebrata; Class: Aves; Habitat: Aerial

A bird is adapted for an aerial habitat, as it has wings and feathers. It is also adapted to land, as it is bipedal (two rear limbs). Birds are warm blooded and their body is divided into the head, neck and trunk. The trunk is divided into the thorax and abdomen.

A bird has a strong skeleton. Birds have pneumatic bones that are hollow, and light in weight. This feature enables them to fly in air. Furthermore, a streamlined body also helps it to cut through air. The forelimbs are modified into wings which enable it to fly. The hind limbs are long and have toes and claws, which help to hold food, and hold onto branches.

Birds have a four chambered heart and well developed lungs that have air sacs attached to them. The air sacs help birds in respiration. The upper and lower jaws are modified into a horny beak without teeth. Birds have a large muscular stomach and are oviparous, that is they lay yolked, hard-shelled eggs.

Specific features of Phylum Chordata (Class: Aves)

  • Birds are vertebrates.
  • They have a strong skeleton, modified for flight, along with wings and feathers.
  • Birds are warm blooded like other members of the class Aves.


  • The forelimbs are modified into wings for flying in air.
  • The hind limbs are adapted to walk, swim, perch, and hold food.
  • The layers of feather provide insulation and protect the birds from different weather conditions and keep them warm.
  • The muscles are well developed which helps them in flight.
  • The bones are pneumatic, which means they are hollow and light.  This aids flight due to reduced bone weight.
  • They have high sense of hearing and sharp eyesight, which helps them to locate food from a distance.
  • They posses extraordinary communication and song producing abilities.

Learning Outcomes

  1. Students understand the terms Invertebrates and Vertebrates.
  2. Students understand the features of different animal phylums.
  3. Students understand the adaptations of animals.

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